Polycyclic aromatic hydrocarbons are solid materials with low volatility. Polycyclic aromatic hydrocarbons are fat soluble and are generally believed to be carcinogenic, mutagenic and teratogenic (cause deformities). Several hundred polycyclic aromatic hydrocarbons have been identified in creosote, the combustion product of petrochemicals and wood, and in asphalt. Some common examples of polycyclic aromatic hydrocarbons include: naphthalene, methylnaphthalenes, acenaphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthrene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(j)fluoranthene, benzo(k)fluoranthene, benzo(e)pyrene, benzo(a)pyrene, perylene, indeno[123-cd]pyrene, dibenzo(a,h)anthracene, and benzo(ghi)perylene.
StructureBenzo(a)pyrene Benzo(e)pyrene Benzo(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(j)fluoranthene Benzo(k)fluoranthene Dibenzo(a,h)anthracene
Unfortunately, polycyclic aromatic hydrocarbons have a low degradation rate and tend to prevail in creosote and asphalt over extender periods of time. Since polycyclic aromatic hydrocarbons present potential health concerns, it is desirable to reduce the level of human and environmental exposure to such compounds by removing them from or sequestering them in materials where they are present, such as asphalt, creosote, and rubber or plastic products. This is a particularly important objective in cases where products made with materials containing polycyclic aromatic hydrocarbons come into close proximity to humans and/or the environment during manufacturing or during the service life of the product. For instance, recent European legislation requires that extender oils utilized in manufacturing tires for sale in Europe contain no more than 1 mg/kg of benzo(a)pyrene. Accordingly, the amount of polycyclic aromatic hydrocarbons present in a manufactured product can, in some cases, be limited by reducing the quantity of polycyclic aromatic hydrocarbon-containing material incorporated into the product during manufacturing. However, elimination of all PAH or reduction of PAH content to very low levels may not be possible in cases where polycyclic aromatic hydrocarbons are inherently present in the material, such as in asphalt and creosote containing products.
The use of coal-tar creosote on a commercial scale began the early part of the 19th Century after the pressure treatment of wood with coal-tar creosote was developed by John Bethell. This process was originally known as the “Bethell process” and is generally referred to today as the fuel-cell process. In any case, it involves sealing wood in a pressure chamber and applying a vacuum to remove air and moisture from the wood cells. The wood is then pressure treated to impregnate it with the creosote. After this pressure treatment vacuum is normally applied to remove excess creosote from the wood being treated.
In the early 20th century the empty-cell process for treating wood with creosote was developed. This process involves compressing air inside the wood so that the creosote preservative can only coat the inner cell walls rather than saturating the interior cell voids. The empty-cell process is a less effective than the fuel-cell process, but is used because it requires less of the creosoting preservative to treat the same quantity of wood. In any case, important uses for creosote treated wood include railroad ties or sleepers, utility poles (telephone poles and power line poles), ground pilings, marine pilings, and fence posts. However, creosote treated wood can be advantageously employed in a wide variety of applications where toxicity to fungi, insects, and marine borers is desired. Creosote also serves beneficially in many applications as a natural water repellant.
U.S. Pat. No. 5,656,041 discloses a process for detoxifying a coal-tar deposit comprising: adding at a mixing station effective amounts of carbon and a calcium oxide containing substance to at least a portion of said coal-tar deposit, thereby forming a reaction mixture; and mixing said reaction mixture at a temperature of from about 70° F. to about 130° F. for a time sufficient to detoxify the reaction mixture and convert it into a non-hazardous reaction product.
U.S. Pat. No. 4,977,871 discloses a system for the selective removal of polynuclear aromatic hydrocarbons containing 3 or more aromatic rings from lubricating oil used to lubricate the engine of a motor vehicle which comprises activated carbon positioned within the lubricating system and through which the lubricating oil circulates, said activated carbon being selective to removing polynuclear aromatic hydrocarbons containing 3 or more aromatic rings from the lubricating oil.
U.S. Pat. No. 5,069,799 and U.S. Pat. No. 5,225,081 relate to a method for removing polynuclear aromatics from a used lubricating oil which comprises passing the lubricating oil through a filter system containing a hollow solid composite comprising a thermoplastic binder and activated carbon, wherein the composite is formed by the steps comprising (a) providing a quantity of the thermoplastic binder in the form of particles having diameters between about 0.1 and about 250 micrometers; (b) providing a quantity of activated carbon having a softening temperature substantially greater than the softening temperature of the thermoplastic binder, the activated carbon being in the form of particles having diameters between about 0.1 and about 3,000 micrometers; (c) combining the particles from (a) and (b) to form a substantially uniform mixture wherein from about 2 to about 25 weight percent of the thermoplastic binder and about 40 to about 75 weight percent of the activated carbon are present in the mixture; (d) extruding the substantially uniform mixture of (c) into a die; (e) heating the substantially uniform mixture from (d) to a temperature substantially above the softening temperature of the thermoplastic binder but to a temperature less than the softening temperature of the activated carbon; (f) applying sufficient back pressure, from outside the die, to the heated mixture from (e) within the die to convert the heated mixture into a substantially homogeneous composite; (g) rapidly cooling the composite from (f) to a temperature below the softening point of the thermoplastic binder to produce a cooled composite; and (h) extruding the cooled composite from the die as an extruded hollow solid composite.
U.S. Pat. No. 4,100,059 discloses an asphalt recycling method comprising the steps of: (a) introducing (1) asphalt waste and (2) activated terra alba, activated carbon or a mixture thereof into a tank of water; (b) jetting steam into said water to heat said water to a temperature sufficient to soften the asphalt waste; and (c) mechanically subdividing the asphalt waste while immersed in the heated water into aggregate grains, each aggregate having a surface coated with a thin asphalt film.
United States Patent Publication No. 2009/0301931 reveals a cost-effective solution is provided for eliminating refinery process waste, including spent catalytic and non-catalytic adsorbent materials, as well as adsorbate process reject materials derived from desorption, while minimizing conventional waste handling demands. The asphalt composition of United States Patent Publication No. 2009/0301931 includes asphalt and spent adsorbent material from a solvent deasphalting unit. This asphalt can comprise asphaltic material obtained from a solvent deasphalting unit, and spent adsorbent material in the asphalt composition was previously utilized in the solvent deasphalting unit. The asphalt composition of United States Patent Publication No. 2009/0301931 can also include process reject materials.
United States Patent Publication No. 2009/0283012 discloses a process for manufacturing a foamed asphalt composition, said process comprising: (a) comminuting spent, unregenerated activated carbon to particles whose longest dimension is a maximum of about 250 microns; (b) heating said comminuted activated carbon to an elevated temperature of from about 100° C. to about 300° C. to remove therefrom volatile species having boiling points below said elevated temperature; (c) following removal of said volatile species therefrom, exposing said activated carbon to moisture to cause said activated carbon to absorb said moisture to a level of from about 1% to about 25% by weight; and (d) combining said activated carbon with a liquid asphalt composition at a temperature of at least about 120° C. to cause said liquid asphalt composition to foam.